nanopower Buck Converter

Transcription

1 EVALUATION KIT AVAILABLE Click here for production status of specific part numbers. General Description The MAX3864xA/B are nanopower family of ultra-low 330nA quiescent current buck (step-down) DC-DC converters operating from 1.8V to 5.5V input voltage and supporting load currents of up to 175mA, 350mA, 700mA with peak efficiencies of 96%. While in shutdown, there is only 5nA of shutdown current. The devices offer ultra-low quiescent current, small total solution size, and high efficiency throughout the load range. The MAX3864xA/B are ideal for battery applications where long battery life is a must. The MAX3864xA/B family utilizes a unique control scheme that allows ultra-low quiescent current and high efficiency over a wide output current range. MAX38642 excludes active discharge resistor in shutdown which allows the output to be regulated or held high by another source or by the charged output capacitor. The MAX3864xA/B devices are offered in a space-saving 1.42mm x 0.89mm 6-pin wafer-level package (WLP) (2 x 3 bumps, 0.4mm pitch), as well as a 2mm x 2mm, 6-pin µdfn package. All parts are specified from -40 C to +85 C. Benefits and Features Extends Battery Life 330nA Ultra-Low Quiescent Supply Current 5nA Shutdown Current 96% Peak Efficiency and Over 88% at 10µA Easy to Use Addresses Popular Operation 1.8V to 5.5V Input Range Preprogrammed V OUT from 0.5V to 5V Single Resistor Adjustable V OUT from 0.7V to 3.3V ±1.75% Output Voltage Accuracy Up to 175mA/350mA/700mA Load Current Protects System in Multiple Use Cases Reverse-Current Blocking in Shutdown Optional Active Discharge Feature Reduces Size and Increases Reliability -40 C to +85 C Temperature Range 2mm x 2mm 6-pin µdfn Package 1.42mm x 0.89mm, 0.4mm Pitch 6-pin (2 x 3) WLP Ordering Information appears at end of data sheet. Applications Portable Space-Constrained Consumer Products Wearable devices, Ultra-Low-Power IoT, NB IoT, and BLE Single Li-ion and Coin Cell Battery Products Wired, Wireless, Industrial Products Typical Operating Circuit 2.2µH INPUT 1.8V-5.5V OUTPUT 1.8V IN LX OUT C IN 10µF C OUT 22µ F MAX38640A RSEL EN GND R SEL 768kΩ ; Rev 0; 10/18

2 Absolute Maximum Ratings IN, EN, RSEL, NC, OUT to GND V to +6V LX RMS Current WLP A RMS to +1.6A RMS LX RMS Current µdfn... -1A RMS to +1A RMS Continuous Power Dissipation - WLP (T A = +70 C) (Derate 10.5mW/ C above +70 C) mW Continuous Power Dissipation µdfn (T A = +70 C) (Derate 4.5mW/ C above +70 C) mW Operating Temperature Range C to +85 C Maximum Junction Temperature C Storage Temperature Range C to +150 C Lead Temperature (soldering, 10 seconds) ºC Soldering Temperature (reflow) C Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Package Information 6 µdfn Package Code L622+1C Outline Number Land Pattern Number Thermal Resistance, Four Layer Board: Junction-to-Ambient (θ JA ) Junction-to-Case Thermal Resistance (θ JC ) C/W 122 C/W For the latest package outline information and land patterns (footprints), go to Note that a +, #, or - in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer board. For detailed information on package thermal considerations, refer to thermal-tutorial. 6 WLP Package Code N60E1+2 Outline Number Land Pattern Number Refer to Application Note 1891 Thermal Resistance, Four Layer Board: Junction-to-Ambient (θ JA ) C/W For the latest package outline information and land patterns (footprints), go to Note that a +, #, or - in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer board. For detailed information on package thermal considerations, refer to thermal-tutorial. Maxim Integrated 2

3 Electrical Characteristics (V IN = 3.3V, V OUT = 1.8V, T A = -40 C to +85 C, C IN = 4.7µF, C OUT = 10µF, unless otherwise specified. (Note 1)) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Shutdown Current I IN_SD V EN = 0V, T A = 25 C µa Input Voltage Range V IN_RANGE Guaranteed by Output Accuracy V Input Undervoltage Lockout V UVLO V UVLO R SEL > 50kΩ (MAX3864xA), MAX3864xB RSEL < 50kΩ (MAX3864xA) V IN rising V Hysteresis 50 mv V IN rising V Hysteresis 125 mv Output Voltage Range V OUT_RANGE Guaranteed by Output Accuracy V Output Accuracy V OUT_ACC above 1MHz, V OUT = 0.7V to 3.3V, V IN = OUT falling, when LX begins switching 5.5V (Note 2) DC Line Regulation V LREG V OUT = 1.8V, V IN = 2.0V to 5.5V, I OUT = 10mA to 160mA Quiescent Supply Current Into IN Quiescent Supply Current Into OUT I Q_IN I Q_OUT V EN = V IN, not switching V OUT = 106% of target voltage, V OUT TARGET = 2.5V, T A = 25 C V EN = V IN, not switching V OUT = 106% of target voltage, V OUT TARGET = 2.5V, T A = 25 C % ±1.5 % na 10 na Soft-Start Slew Rate dv OUT /dt V OUT = 1.8V, no load 6.5 mv/µs LX Leakage Current I LEAK_LX V LX = V IN = 5.5V, T A = 25 C na Inductor Peak Current Limit High-Side R DSON R DS_H V IN = 3.3V Low-Side R DSON R DS_L V IN = 3.3V Zero-Crossing Threshold I PEAK_LX MAX38641/MAX MAX MAX MAX MAX38641/ MAX MAX MAX MAX38641/ MAX MAX I ZX_LX V OUT = 1.2V, percent of I PEAK_LX 5 % Enable Input Leakage I LEAK_EN V EN = 5.5V, T A = +25 C na Enable Voltage Threshold Active Discharge Resistance ( MAX3860/ MAX3861/MAX3863 Only) V EN_R V EN rising V EN_F V EN falling R OUT_DIS V EN = 0V, Ω ma mω mω V Maxim Integrated 3

4 Electrical Characteristics (continued) (V IN = 3.3V, V OUT = 1.8V, T A = -40 C to +85 C, C IN = 4.7µF, C OUT = 10µF, unless otherwise specified. (Note 1)) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Required Select Resistor Accuracy (MAX3864xA only) Select Resistor Detection Time (MAX3864xA Only) R SEL Use the nearest ±1% resistor from R SEL Selection Table % t RSEL C SEL < 2pF µs Thermal Shutdown T SHUT T J rising when output turns off 165 C Thermal Shutdown Threshold T SHUT T J falling when output turns on 150 ºC Note 1: Note 2: Limits over the specified operating temperature and supply voltage range are guaranteed by design and characterization, and production tested at room temperature only. Output Accuracy in Low Power Mode (LPM) and does not include load, line or ripple. Maxim Integrated 4

5 Typical Operating Characteristics (MAX38640AENT+, V IN = 3.6V, V OUT = 1.8V, L = 2.2μH, C IN = 10μF, C OUT = 22μF, T A = 25 C, unless otherwise noted.) Maxim Integrated 5

6 Typical Operating Characteristics (continued) (MAX38640AENT+, V IN = 3.6V, V OUT = 1.8V, L = 2.2μH, C IN = 10μF, C OUT = 22μF, T A = 25 C, unless otherwise noted.) Maxim Integrated 6

7 Typical Operating Characteristics (continued) (MAX38640AENT+, V IN = 3.6V, V OUT = 1.8V, L = 2.2μH, C IN = 10μF, C OUT = 22μF, T A = 25 C, unless otherwise noted.) Maxim Integrated 7

8 Pin Configurations MAX3864 ELT+ IN 1 6 EN MAX3864--ELT+ LX 2 5 OUT GND 3 4 RSEL/NC MAX3864 ENT A IN LX GND MAX3864--ENT+ B EN OUT RSEL /NC Pin Description MAX3864 ELT+ PIN MAX3864 ENT+ NAME 1 A1 IN FUNCTION Regulator Supply Input. Connect to a voltage between 1.8V and 5.5V and bypass with a 10µF capacitor from IN to GND. 2 A2 LX Switching Node. Connect an inductor between LX and the regulator output. 3 A3 GND Ground. Maxim Integrated 8

9 Pin Description (continued) MAX3864 ELT+ PIN MAX3864 ENT+ NAME 4 B3 RSEL/NC 5 B2 OUT 6 B1 EN FUNCTION MAX3864 A: Output Voltage Select Input. Connect a resistor from RSEL to GND to program the output voltage and IN undervoltage threshold based on the Table 1. MAX3864 B: No Connect. Leave floating. Output Voltage Sense Input. Connect to the load at a point where accurate regulation (output capacitor) is required to eliminate resistive metal drops. Enable Input. Force this pin high to enable the buck converter. Force this pin low to disable the part and enter shutdown. Functional Diagrams INPUT IN CIN 10µF UVLO MAX38640/1/2/3 A/B REVERSE BLOCKING EN CURRENT SENSE MODULATOR LX 2.2µH OUTPUT THERMAL SHUTDOWN OUT COUT 22µF 0.6V REFERENCE OPTIONAL ACTIVE DISCHARGE MAX3864xA ONLY RSEL UVLO AND TARGET OUTPUT SELECTOR RSEL GND Maxim Integrated 9

10 Detailed Description MAX38640/1/2/3 A/B are ultra-low IQ (330nA) buck converters that step-down from 1.8V to 5.5V to wide range of output voltages between 0.5V to 5V. The output voltage is either programmable on MAX3864xA versions using an external resistor or fixed for MAX3864xB versions. The external R SEL resistor on the RSEL pin programs the output voltage upon startup for MAX3864xA versions. The buck converter automatically switches between ultra-low-power mode (ULPM), low-power mode (LPM), and highpower mode (HPM) to better service the load, depending on the load current. The buck converter overregulates in ultralow-power mode to allow the output capacitor to handle the transient load currents. The device has 90% duty cycle limitation. Active discharge resistor in MAX38640/MAX38641/MAX38643 pulls OUT to ground when the part is in shutdown. Active discharge has been strategically omitted for MAX38642 to preserve the charge on the output capacitor in shutdown. Harvesting applications where the output is connected to a super capacitor can take advantage of reverse-current blocking feature to preserve the charge on the output capacitor even if the input were to fall below the output in shutdown. Applications where two MAX38642 buck converters are connected in parallel to the drive the load can have the input of one of the buck converters to go to 0V in shutdown without dragging the output down or loading the other buck. Maxim Integrated 10

11 Voltage Configuration The MAX3864xA includes an RSEL pin to configure the output voltage and input UVLO threshold on startup. Resistors with tolerance 1% (or better) should be chosen, with nominal values specified in Table 1. Table 1. MAX3864xA RSEL Selection Table TARGET OUTPUT VOLTAGE (V) R SEL (kω) INPUT UVLO THRESHOLD, RISING (V) 2.5 OPEN Maxim Integrated 11

12 Table 1. MAX3864xA RSEL Selection Table (continued) TARGET OUTPUT VOLTAGE (V) R SEL (kω) INPUT UVLO THRESHOLD, RISING (V) SHORT TO GND 2.6 The MAX3864xB has a fixed output voltage that is preprogrammed (no RSEL programming). Contact Maxim to order a part with an output voltage listed in Table 2. The input UVLO threshold for MAX3864xB is 1.75V (typ., V IN rising) with 50mV hysteresis (typ.). Table 2. MAX3864xB Preprogrammed Output Voltage Table PART NUMBER OUTPUT VOLTAGE (V) MAX3864xB MAX3864xB MAX3864xB MAX3864xB MAX3864xB MAX3864xB MAX3864xB MAX3864xB MAX3864xB MAX3864xB MAX3864xB MAX3864xB MAX3864xB MAX3864xB MAX3864xB MAX3864xB MAX3864xB MAX3864xB MAX3864xB Maxim Integrated 12

13 Applications Information Inductor Selection The inductor value for MAX3864x affects the ripple current, the transition point from low power mode (LPM) to ultralow-power mode (ULPM), and the overall efficiency performance. Based on the peak current limit required for different applications, it is recommended to select an inductor value based on Table 3. Table 3. Inductor Selection PEAK CURRENT, PART NUMBER 1.0A Peak Current, MAX mA Peak Current, MAX38641/MAX mA Peak Current, MAX INDUCTANCE RANGE (µh) Input Capacitor The input capacitor (C IN ) reduces the peak current drawn from battery or input power source and reduces the switching noise in the IC. The impedance of C IN at the switching frequency should be very low. Ceramic capacitors are recommended with their small size and low ESR. For most applications, use 10µF ceramic capacitor with X5R or X7R temperature characteristics. Output Capacitor The output capacitor (C OUT ) is required to keep the output voltage ripple small and to ensure loop stability. C OUT must have low impedance at the switching frequency. Ceramic capacitors are recommended due to their small size and low ESR. Make sure the capacitor does not degrade its capacitance significantly over temperature and DC bias. Capacitors with X5R or X7R temperature characteristics typically perform well. A 22µF ceramic capacitor is recommended for most applications. Enabling Device The device has a dedicated EN pin. This pin can be driven by a digital signal. It is recommended that the digital signal enables the device after V IN crosses the UVLO threshold. In applications where EN is tied to IN, the device is designed to be powered by fast V IN slew rates. If V IN slew rates are slower than 5V/ms, users must delay enabling the device after V IN crosses the UVLO threshold. This can be done using a simple RC circuit, as shown in Figure 1. IN BAT54 REN EN CEN Figure 1. RC Circuit at EN Maxim Integrated 13

14 PCB Layout and Routing High switching frequencies and large peak currents make PCB layout a very important part of the buck regulator design. Good design minimizes excessive EMI (Electromagnetic Interference) on the feedback paths and voltage gradients in the ground plane, to avoid instability and regulation errors. The input capacitor (C IN ) should be placed as close as possible to the IC pins IN and GND. Connect the inductor, input capacitor, and output capacitor (C OUT ) as close together as possible, and keep their traces short, direct, and wide. Connect the two GND pins under the IC and directly to the ground of the output capacitor. Keep noisy traces, such as the LX node, as short as possible. The OUT pin should be connected to the output capacitor and this trace should be routed away from the main power path between the inductor and C OUT. The OUT trace should also be routed away from noisy traces such as the LX line or other external noise sources. Refer to the MAX3864x evaluation kit for an example PCB layout and routing scheme. Ordering Information PART NUMBER PEAK INDUCTOR CURRENT (A) ACTIVE DISCHARGE FEATURES PACKAGE MAX38640AELT+* 0.25 Yes MAX38641AELT+* 0.50 Yes MAX38642AELT+* 0.50 MAX38643AELT+* 1.00 Yes 0.7V to 3.3V Resistor-Selectable Output Voltage Using RSEL (Resistor Select) Pin 6-pin 2mm x 2mm μdfn MAX38640BELT+* 0.25 Yes MAX38641BELT+* 0.50 Yes MAX38642BELT+* 0.50 MAX38643BELT+* 1.00 Yes MAX38640AENT Yes MAX38641AENT+* 0.50 Yes MAX38642AENT+* 0.50 MAX38643AENT+* 1.00 Yes MAX38640BENT+* 0.25 Yes MAX38641BENT+* 0.50 Yes MAX38642BENT+* 0.50 MAX38643BENT+* 1.00 Yes *Future product contact factory for availability. +Denotes a lead(pb)-free/rohs-compliant package. T Denotes tape-and-reel. 0.5V to 5V Preprogrammed Output Voltage 0.7V to 3.3V Resistor-Selectable Output Voltage Using RSEL (Resistor Select) Pin 0.5V to 5V Preprogrammed Output Voltage 6-pin 2mm x 3 0.4mm Pitch WLP Maxim Integrated 14

15 Revision History REVISION NUMBER REVISION DATE DESCRIPTION PAGES CHANGED 0 10/18 Initial release For pricing, delivery, and ordering information, please visit Maxim Integrated s online storefront at Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc Maxim Integrated Products, Inc.